Pascal Parser in Python

This project is an example on how to use parol-pygen in praxis. The used input grammar description pascal.par uses %grammar_type 'LALR(1)' directive to instruct parol to use an LR parser algorithm.

This project shows a scaffolded parser project generated by parol-pygen init.

Setup after fresh clone

This project requires Python 3.10+ and uses a local virtual environment in .venv.

Script variants are available for both platforms:

• PowerShell: scripts/*.ps1
• Bash: scripts/*.sh

Prerequisites

1. Install Python >=3.10.

2. Install uv (recommended).

3. Verify tools are available:

   python --version
   uv --version

   On Windows a global python installation may also be accessible via py launcher utility which is sufficient for our purpose.

   py --version

Recommended workflow with uv

From the repository root:

If you are on Linux/macOS, make scripts executable once:

chmod +x ./scripts/*.sh

1. Bootstrap the local environment:

   ./scripts/bootstrap.ps1

   ./scripts/bootstrap.sh

   This script:

   • creates .venv (if missing) via uv venv .venv
   • installs dependencies via uv sync
   • resolves parol-pygen from PyPI according to pyproject.toml

2. Activate the virtual environment (optional but convenient for manual commands):

   .\.venv\Scripts\Activate.ps1

   source .venv/bin/activate

3. Generate parser code:

   ./scripts/generate-parser.ps1

   ./scripts/generate-parser.sh

4. Run the proof/example parser:

   ./scripts/run-proof.ps1 .\basics.pas

   ./scripts/run-proof.sh ./basics.pas

You can also run tools through uv without activating the environment, for example:

uv run python .\proof_runner.py .\basics.pas

uv run python ./proof_runner.py ./basics.pas

Alternative workflow with venv + pip

If you cannot use uv, you can still set up a working environment manually:

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install -e .

How this was created

1. Generate the export JSON pascal_export.json using Parol CLI:

   parol export -f .\pascal.par -o .\pascal_export.json --pretty

   To be able to use the Parol CLI, you should additionally install Parol, e.g. using cargo:

   cargo install parol

2. Run ./scripts/bootstrap.ps1 or ./scripts/bootstrap.sh

3. Run ./scripts/generate-parser.ps1 or ./scripts/generate-parser.sh

4. Run ./scripts/run-proof.ps1 or ./scripts/run-proof.sh

Example:

PowerShell: ./scripts/run-proof.ps1 .\basics.pas

Bash: ./scripts/run-proof.sh ./basics.pas

Generated package

• Package name: pascal_py
• Entry parser class: pascal_py.Parser
• User semantic action base: pascal_py.UserActions